Right, the M9 doesn't have the controls, just a single button. Personally I prefer the PR100/200 to the M9 (and the ADDIEM) but they might sound a bit too calm after the CX300. Balance is very good on ECCI earphones and they roll off gently on either end - no monster bass or hyped-up treble there (in stark contrast to the M9 and S4). Plus they have a thick presentation which may make them boring to some. The ADDIEMs sound much thinner and crisper. They are more detailed than the PR100/200 and have better clarity but they don't round off notes as well and sound a bit too analytical and artificial for their own good.

All of these are an improvement from the CX300 in my book but you may need time to adjust after the warm and muddy Senns.

Not sure if you want other suggestions but mp4nation is currently selling the Brainwavz M1 for $29.50 shipped which is a killer deal.